Aging Auditory System: Presbycusis and its Neural Bases: The process of aging in modern, technologically advanced societies is accompanied by hearing impairment known as presbycusis. This age-related disorder often causes significant communication problems in person who have had no previous hearing or speech deficits, resulting in impaired relationships at home and in the workplace, as well as increased costs to the individual, families and society. After reaching 60 years, the percentage of the population experiencing difficulty in perceiving speech doubles per decade, 16% at 60, 32% at 70, 64% at 80, and virtually all of the population beyond 85 years of age. The major goal of this proposal is to increase our knowledge of auditory processing deficits of presbycusis and to advance our understanding of its neural bases. A thematic focus is applied to distinguishing the effects of peripheral and central nervous system aging effects. This proposal puts forth a five-year series of interrelated hypothesis tested with tightly coupled and truly interdisciplinary experimental and clinical methodologies. These investigations in mammals examine both human and animals populations. Disciplines of neuroimaging, psychoacoustics, audiology, evoked potentials, and reflex psychology are brought to bear on testing hypothesis in human subjects. Scientific disciplines of reflex psychology, evoked potential and single-unit neurophysiology, neuroanatomy, neuroimaging, and cellular physiology will test hypothesis utilizing animal populations. Comparisons will be made between young, middle-age and elderly subject groups to determine aging effects in hearing loss, and comparisons will be made between subjects with cochlear sensitivity losses and those with normal hearing to assess the effects of peripheral hearing loss. Special attention will be given to interdisciplinary, repeated- measure experimental designs, quantitative multivariate data analyses, in determining the effects of different types of background noise on neural and perceptual processing. The goal of this hypotheses-testing thrust concerning the neural bases of age-related hearing los is to contribute knowledge that eventually leads to medical interventions that prevent, alleviate or minimize the hearing and communication problems with presbycusis.